Switch devices of this kind are intended more particularly to provide safety for personnel concerned with supervising, controlling or maintaining an installation extending over a considerable length along which the cable is tensioned. In the event of danger, the personnel apply a deflection to the cable to pull the movable assembly against the return force exerted by the spring. One of the groove flanks encounters the actuating member and this actuates the switch.
Amongst the malfunctioning to which devices of this kind may be subject we should first mention unintentional deflection to which the cable may be subjected when an operator comes into contact with it involuntarily. It is desirable that such involuntary deflection should not result in actuation of the switch. The same applies to quick deflections due to unauthorized use, to simulate a breakdown.
Another disorder to which such devices are subject is due to the elongation or shrinkage of the cable due to heat as a result of temperature variations in the cable environment. Variations of the order of 10.degree. C. are in no way exceptional in any latitude, resulting in a steel cable 30 m long having length variations of the order of 3.5 mm.
It has also been found that inadequate tension of the cable allows very low frequency oscillations to develop, the amplitude of which may be sustained or increased in response to pulses due, for example, to the wind. When a certain amplitude is reached the result is abnormal actuation of the switches even in the absence of nearby staff.
The various factors which are likely to result in undesirable actuation of the switches therefore shows that the adjustment of such a device is relatively complex despite its apparent simplicity, and it is advisable to provide the installation engineer with adjustable such devices to allow for accommodation of the influence of the various parameters mentioned above.